This invention relates to a metallic core of a rubber track used for moving construction machinery and construction working machinery.
Recently rubber tracks have been progressively widely used for agricultural machinery as well as construction machinery and construction working machinery in place of iron shoe tracks which had been used as traveling devices for construction machinery and construction working machinery.
In general, the rubber track includes an endless belt-shaped rubber-like elastic member, a number of metallic cores embedded therein and aligned in the longitudinal direction thereof and extending in traverse directions thereof, and steel cords (tension-resistant members) embedded in the endless elastic member to surround the metallic cores circumferentially outwardly. As such rubber tracks are made of rubber-like materials, vibrations transmitted to personnel are mitigated and paved roads are not damaged. Therefore, rubber tracks have been used widely.
In recent years, particularly, large type rubber tracks have been developed for use in construction machinery. It is often required to use such rubber tracks in substitution for iron shoe tracks for construction machinery which has been equipped with iron shoe tracks. In order to fulfill the requirement, therefore, the rubber tracks have a particular configuration and various attempts have been made especially in metallic cores embedded in rubber tracks. In general, a number of metallic cores are embedded in a rubber track with constant intervals, and the metallic cores are provided with protrusions projecting into the inside of the rubber track for rolling on lower idlers of the machinery.
On the other hand, the machinery body of several tons is supported by the ten or more lower idlers so that they are subjected to a heavy weight. With this construction, therefore, the metallic cores rock about their longitudinal axes due to the weight every time the lower idlers have just ridden on the protrusions of the metallic cores and transferred onto adjacent metallic cores. As a result, the lower idlers are repeatedly raised and lowered at the metallic cores and between the metallic cores as a whole, so that vibrations are transmitted to a personnel on the machinery due to the upward and downward movement of the lower idlers.
In view of this, a metallic core 1 as shown in FIG. 1 has been proposed, whose protrusions 2 have curved top surfaces 3 depressed at their centers, on which the lower idlers roll. This construction is intended to mitigate the vibrations by reducing the difference between the rocking movements of the metallic cores about their axes and the vertical movements of the lower idlers.
As shown in a traveling device or a vehicle in FIG. 2, however, the rubber track extends around a driving wheel 4 and an idler 5 to be driven by the driving wheel 4. The upper part of the rubber track moving on the side of the vehicle body 6 is supported by upper idlers 7 mounted on the vehicle body 6. However, the upper idlers 7 are generally metallic rollers which support the metallic cores 1 embedded in the rubber track by contacting the top surfaces 3 of the protrusions 2 of the metallic cores 1.
Therefore, if the top surfaces 3 of the protrusions 2 are concave as described above, the upper idlers repeatedly collide directly against the ends of the protrusions 2 to produce annoying noise and cause damage to the protrusions or the upper idlers as the case may be. This failure results from the concave top surfaces 3 of the protrusions 2 taking into consideration only the contact with the lower idlers 8 without taking into account the upper idlers 7. In this case, the ends of the upper surfaces 3 of the protrusions 2 aid in increasing the violence of collision of the metallic cores 1 against the upper idlers 7.
Another example of metallic cores of a rubber track hitherto used for construction machinery and the like is shown in a plan view of FIG. 3 and a sectional view of FIG. 4. In these drawings, the metallic core has wing portions 11 to be embedded in a rubber-like elastomer and an engaging portion 12 adapted to engage teeth of a sprocket as a driving wheel. The engaging portion 12 is generally rounded so as to match the teeth of the sprocket and in the form of an inverted-U whose cross-sectional area is narrower than that of the wing portions 11. The metallic core is formed with a pair of protrusions 13 extending from the inner surface of the rubber track and on both sides of the engaging portion 12.
The protrusions 13 serve to prevent the metallic core from removing from an idler 14 provided on the construction machinery, and the top surfaces 15 of the protrusions 13 form traveling surfaces on which the idler 14 rolls. In general, the protrusions 13 are provided with extensions 16 further projecting from the wing portions 11 in longitudinal directions of the rubber track. The top surfaces 17 of the extensions 16 are gently inclined surfaces. The top surfaces 17 may be flat which are flush with the top surfaces 15 of the protrusions 13.
In the metallic cores 11 shown in FIGS. 3 and 4, when the idler 14 arrives at the position A or begins to ride on the top surfaces of the protrusions 13, while rolling on the upper surfaces 15 of the protrusions 13, the weight of the machinery acts on the extensions 16, in the form of a cantilever of the protrusions 13. It is unavoidable for the metallic core to tilt (shown in dot-and-dash lines) in the direction shown by an arrow X in FIG. 4. At this moment, the idler 14 tends to sink somewhat, while tilting together with the metallic core. When the idler 14 arrives at the position B or at the center of the upper surfaces 15 of the protrusions 13, the idler 14 returns to its original level. When the idler 14 arrives at position C or on the extensions 162, the metallic core tilts (shown in two-dot-and-dash lines) in the direction shown by an arrow Y due to the weight of the machinery in the same manner as at the point A, and the idler 14 again sinks.
The above phenomenon is summarized as follows. The idler 14 rolls on the metallic cores, while moving upwardly and downwardly and hence vibrations always occur which are transmitted to personnel. The prevention of the vibrations has been an urgent problem.
Moreover, even if all the top surfaces of a metallic cores are flat, the sinking of the idler could not be avoided. In this case, furthermore, when the idler transfers from the upper surfaces of one metallic core to those of the adjacent metallic core, it is impossible to avoid a collision of the idler against the ends of the extensions of the metallic core. Therefore, strange sounds and additional vibrations are produced by such collisions.
A further example of hitherto used metallic cores is shown in a plan view of FIG. 5, wherein the metallic core is formed with extensions 26 of protrusions 23 projecting from wing portions 11, one extension 26 in one longitudinal direction of a rubber track and the other extension 26 in the opposite direction thereto. In this example, the top surfaces of the protrusions 23 may be gently inclined as shown in FIG. 4 or they may be flat. With this construction, the idler (not shown) preferably continuously rolls alternately on the top surfaces 25 on both sides of the metallic cores. However, there still is the sinking of the idler and the collision of the idler against the extensions 26 of the protrusions 23. Therefore, it is still required to prevent vibrations caused by sinking and collision.
As can be seen from the above explanation, in the large type rubber tracks used in large type construction working machinery such as bulldozers and power shovels, metallic cores tend to tilt about their axes when the idler passes on the metallic cores. The repeated tilting of the cores cause vibrations troublesome to personnel and give rise to cracks in rubber track made of an elastomer and damaging thereof, thereby considerably shortening the service life of the rubber track.